无法从服务器通过 SMTP 发送邮件，但我可以从本地主机发送邮件

Question

当我尝试在我的 Java 应用程序中通过 SMTP 发送电子邮件时，我收到以下信息。我是运行我的 Windows Server 2012 R2 上的胖 JAR 中的 Springboot 应用程序。

Whitelabel Error Page

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sun Apr 09 22:16:57 CEST 2017
There was an unexpected error (type=Internal Server Error, status=500).
Mail server connection failed; nested exception is com.sun.mail.util.MailConnectException: Couldn't connect to host, port: internetsmtp.test.com, 25; timeout -1; nested exception is: java.net.UnknownHostException: internetsmtp.test.com. Failed messages: com.sun.mail.util.MailConnectException: Couldn't connect to host, port: internetsmtp.test.com, 25; timeout -1; nested exception is: java.net.UnknownHostException: internetsmtp.test.com

代码：

public void sendEmail(String from, String replyTo, String to, String subject, String body) {
        final Email email;
        try {
            email = DefaultEmail.builder()
                    .from(new InternetAddress(from))
                    .replyTo(new InternetAddress(replyTo))
                    .to(Lists.newArrayList(new InternetAddress(to)))
                    .subject(subject)
                    .body(body)
                    .encoding("UTF-8").build();
            emailService.send(email);
        } catch (AddressException e) {
            log.error("MailUtil got exception while sending mail = " + e.getMessage());
        }
    }

application.properties:

# Server
server.port=8080

# Mail Config
spring.mail.host: internetsmtp.test.com
spring.mail.port: 25
spring.mail.username: user123
spring.mail.password: test123
spring.mail.properties.mail.smtp.auth: true
spring.mail.properties.mail.smtp.starttls.enable: false
spring.mail.properties.mail.smtp.starttls.required: false
spring.mail.persistence.enabled: false
spring.mail.persistence.redis.embedded: false
spring.mail.persistence.redis.enabled: false
spring.mail.scheduler.priorityLevels=10

我什至试过信任证书:

keytool -import -file "C:\mail.cer" -keystore "C:\Program Files\Java\jre.1.8.0_121\lib\security\cacerts" -alias mail

我可以从 localhost 毫无问题地完成所有这些工作。是否可能是我的服务器阻止了与 SMTP 服务器的连接？

Answer 1

您的例外清楚地说明 - java.net.UnknownHostException: internetsmtp.test.com。这意味着（在这种情况下）您的应用程序无法从服务器解析 DNS 名称。确保您能够从服务器本身 ping 该域，并且该服务器的 DNS 访问（端口 53）未被阻止

Answer 2

很可能是防火墙阻止了直接连接。 JavaMail FAQ 有更多 tips for debugging connection problems.

无法从服务器通过 SMTP 发送邮件，但我可以从本地主机发送邮件

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